Update Dependabot configuration to ignore JUnit v6

Signed-off-by: Dariusz Jędrzejczyk <dariusz.jedrzejczyk@broadcom.com>

Author: chemicL

.github/dependabot.yml

@@ -30,6 +30,14 @@ updates:
       - dependency-name: "ch.qos.logback:logback-classic"
         versions:
         - ">= 1.3.a"
+      # JUnit: don't upgrade to v6 (requires JDK17+)
+      - dependency-name: "org.junit:*"
+        versions:
+          - "[6.0.0,)"
+      # JUnit Jupiter: don't upgrade to v6 (requires JDK17+)
+      - dependency-name: "org.junit.jupiter:*"
+        versions:
+          - "[6.0.0,)"
       # TestNG: 7.6+ doesn't support JDK8 anymore
       - dependency-name: "org.testng:testng"
         versions: